In some ways, Russia's veto isn't surprising. As the New York Times notes, Russia objected to the resolution when it was being drafted. It has also blocked similar measures in the past.

But the day before the U.N. vote, Russian President Vladimir Putin called for a U.N. investigation into the incident –– though he blamed the incident on rebels, not Assad.

Russia was reportedly in the process of proposing its own Syrian resolution. But that one would have condemned the U.S. missile strikes ordered by President Donald Trump in response to the chemical attack.